This research is to study the mechanisms by which a peptide angiotensin II, acts in the brain to produce a drinking behavior and at the same time a pressor response and hormone release from the pituitary. The involvement of brain angiotensin in hypertension will be studied by use of spontaneously hypertensive rats (SHR) and their controls, Wistar Kyoto rats (WKY). We propose a testable hypothesis that angiotensin acts as a neurotrigger chiefly, but not exclusively, in the anterior third ventricle region for activating circuits involved in these responses. Ultimately, we would like to study the whole pathway from the synthesis and release of angiotensin, the binding of the peptide to neurones which are biologically activated by angiotensin, and the localization of connections of such effector neurones; how they are mediated by neurotransmitters at each synapse and how they produce these effects. With this goal in mind, it is proposed to map the distribution of angiotensin II-containing neurons with immunocytochemistry in WKY and SHR, to study the effects of angiotensin, other peptides and catecholamines on cells by micriontophoresis in these rat brains, to trace with HRP the efferents from these sites back to the cell bodies and apply the same procedures where those cells are concentrated. Brain slice will be used for intracellular recording and identifying the cells involved. The significance of this research is threefold: Peptides are now recognized as an important new class of neural function modifiers and this research may show how a peptide acts in the brain and how angiotensin contributes to water balance and blood pressure in normal rats and maintained hypertension in SHR. The dipsogenic property of angiotensin is important to study as a key to understanding how fluid balance may be controlled. It is relevant to motivation and behavior as well as disease states such as hypertension.